North American Mesoscale Model Verification on January 26-27...

The North American Mesoscale Model (NAM) is a high resolution model courtesy of the National Center for Environmental Prediction. Another very common and referenced name for the model is the Weather Research and Forecasting Model (WRF). They are the same model and run out to 84 hours. The purpose of the model is to run a higher resolution determining mesoscale features that often cannot be picked up by the global models due to their larger scale. The NAM can be run on an 80km resolution with a broad view of the United States, or 40km which allows the viewer to zoom in on a localized region to put up on mesoscale features. Also a very high resolution form of the NAM exists using a 12km parametric and can zoom into different states. The model is released four times a day at 0z, 6z, 12z, and 18z. Keep in mind that time is zulu or more commonly known as greenwich mean time.

Computer models are critical to forecasting the weather as they use parametric and other mathematical equations to derive the current and predicted state of the atmosphere using a physical and chemical explanation as the background for the predictions. The NCEP is associated with the National Oceanic Atmospheric Administration (NOAA) to be the developer of these computer models. Each meteorological organization worlwide uses their own developed computer models to serve as a basis for the forecasts. Without computer models, we are not able to derive predictions on the weather greater than 24 hours out.

Like all computer models, the NAM shows all layers of the atmosphere in maps determining positioning and speed of the jet stream, surface precipitation amounts (quantitive precipitation forecast QPF), temperatures throughout the entire core of the atmosphere, convective indices, simulated radars, etc. Due to the higher resolution of the NAM, several problems do exist. It often produces convective elements in many middle latitude cyclones and these are known as convective feedback problems. This is where it developed these unstable regions and often associates them as surface lows causing the surface depiction to be distorted. This was a problem in the recent prediction of the January 26-27 winter storm and will be noted below. Also the NAM has a tendency to produce higher than normal precipitation amounts. I typically find myself cutting totals nearly by 30% as shown on the NAM. Finally the NAM has a bias to overamplify a low pressure and close them off to early particularily on eastern United States cyclogenesis off the coast.

The January 26-27 winter storm featured many model headaches do to some interesting variables. Early on it appeared likely for a low pressure to track up inland along the coastal plain. There was a lacking 50/50 low, unfavorable position of the western trough axis, neutral NAO, natural baroclinicity along the coastline, and stale antecedent cold air mass. This would produce rain along I-95 with heavy snows inland. The 500mb synoptic pattern showed very strong signals for this time of setup with most computer model guidance also in support. The GGEM and ECMWF led the pack with the heavy snows from I-81 on westward. The GFS suffered major problems with varying solutions for each run. But then the computer models began to delay the storm. In fact it was delayed nearly 48-60 hours from the original starting time. This caused a different scenario to unfold. The lacking high pressure to the north was still a problem as the anticyclone zoomed east-northeast, but now a high pressure and associated shortwave out ahead of it allowed sunk east-southeast across the Midwest and western Great Lakes. This acted as a 'kicker' helping to push the cyclonegenesis farther off the coast. This in turn allowed for a colder scenario along with precipitation to occur farther east. Therefore a turn of events allowed for a major I-95 snowstorm with 6in+ totals from Washington DC to Boston. This was very fortunate for snow lovers in that corridor due to pure luck given the poor synoptic setup.

Given the NAM's high resolution, it often overanalyzes prognostics post hour 60. It tends to enhance QPF, overamplify lows, and pick up on mesoscale features that really do not exist. Therefore I typically throw out hours 60-84. It would be a rare event where you would find the NAM 84 hour verifying anywhere close to accurate. But in the near term range, the NAM does an excellent job locating temperature thermals, QPF ranges, and picking up on mesoscale features; coastal fronts, enhanced convection, deformation bands, etc. But in this recent storm, it suffered a plethora of problems and even the 6 and 12 hour surface maps had poor verification especially in the QPF department.

Let us first look at the actual accumulated precipitation totals for the storm.Given this is a 24 hour accumulated precipitation amount, about .01-.1in of additional precipitation fell south of the Mason-Dixon line in the previous 24 hours.

Here are the preceeding NAM total QPF forecasts...

(January 24; 18z) (January 25; 6z)

(January 25; 12z) (January 25; 18z)

(January 26; 0z) (January 26; 6z)

As you can see, the NAM had a lot of variance with the northwestern sharp precipitation gradients. These tight gradients this year have been caused by the rapid intensification of the coastal lows allowing the heaviest moisture to be confined closer to the center of circulation. Also in this instance, a very cold and dry air mass along with associated cold front was quickly advancing southeast across the Great Lakes and was even picked up on by the 700mb RH charts. This allowed the flow out of the northwest to dry up some moisture for areas more inland.

The NAM simulated radar vs. the forecast QPF did not match up. Often the NAM simulated radar showed the heavier mesoscale bands lining up in northern Maryland and southern Pennsylvania where as it only showed total QPF to be .25in-.5in. In fact looking at total verification, the NAM did very well for its simulated radar.

(Actual NEXRAD National Radar) (6z NAM January 26 Simulated Radar)

The NAM did seem to have a hold on the 500mb map showing the negatively tilted trough producing the coastal low along with the placement of the upper level low and associated shortwave kicker just to the west.

(18z NAM January 24; 500mb) (0z NAM January 26; 500mb)

In general the differences in the 500mb maps were very subtle with just a general strengthening in the closed 500mb low, which verified a tad north of the January 24 18z model run.

The NAM did a very excellent job in identifying mesoscale band using the UUV/700mb RH charts.(6z NAM January 26; 700mb)

It indentifed the enhanced snow growth over southeastern Pennsylvania up through New Jersey and New York City. The problems with the NAM generally existed in the QPF fields. The model likely suffered a very convective feedback issues in QPF totals. This is why it is important to note other maps than surface maps to help locate the heaviest precipitation. The 700mb map screamed that snow totals would be farther inland with the enhanced deformation band and UUV rates. In general the high resolution models handled this the best with the HRR scoring an amazing victory for QPF along with the ECMWF. The GFS/NAM did a very poor job for QPF, but as noted above QPF does not always tell the story. Sometimes it is important to note other layers of the atmosphere to help make a forecast. This point is why many forecasters missed the boat. Many forecasters (especially broadcoast meteorologists) are drawn to the easy to understand QPF/surface maps, but one has to look at all layers of the atmosphere to make a prediction.

Blizz - it is a good thing we warmed up this afternoon and most of the ice fell from the trees and roofs. Especially the trees. the wind is really whipping and if there were still ice on the trees we would have a big disaster.

I don't think we're done by a long shot. Models spent most of December showing warming into January and that simply did not happen. Even if we're warming up for a few weeks in February into early March, I think we're going to pay for that break in Mid-Late March and Early April.

At least this is my hope. Here in the LSV we've had marginal snow, but exceptional cold. It's definitely been a harsh winter, but not a back-breaker. I know the same cannot be said just 100 miles to our East.

Quoting originalLT:Well GTOsnow, this next one coming up the coast late FRI/SAT., is now positioned by the GFS very close to the coast thus rain or a rain/snow mix. If it actually does wind up coming up the coast a little further East, which could happen, by say 100 miles or so, we could have a snow event ,even for those of us near I95.

Even if winter's almost over, I can't complain. This year has far exceeded my expectations from last fall. Only regret would be not getting out to the Poconos to hit the slopes.

Yeah, F1, we'll have to watch the models to see if the low will trend back to the east or not. Still have time. The models didn't get this last storm too perfectly, it wound up at least centered 200 miles further West than the model runs showed 2-3 days befor the actual event. Of course, that being said,the next one could move further West too!

Quoting GTOSnow:Everyone seems to be thinking this was the last hurrah for us this winter. I keep hearing about pattern changes and how the next two storms we are getting are bringing us all rain.

Anyone care to elaborate?

Sure. Pardon Me Pete (groundhog from my garden) did not see his shadow which according to the Farmers Almanac..."clouds portended warmth and rain that would thaw out the fields and have them ready for planting". So there you have it. It's not rocket science. hahahahahahaahaha

Well GTOsnow, this next one coming up the coast late FRI/SAT., is now positioned by the GFS very close to the coast thus rain or a rain/snow mix. If it actually does wind up coming up the coast a little further East, which could happen, by say 100 miles or so, we could have a snow event ,even for those of us near I95.

The Iceing was pretty bad this morning, couldn't even open the car door!. But now the main roads are good, the temp. is up to 37F. My driveway is still a mess along with the smaller side streets. Walk-ways are dangerous.LT Stamford CT.

Hi LT, nope I don't think I said 7" unless there was a typo in there somewhere. I would've put a guess out at around 12" and that report confirms it I suppose. Classes were cancelled yesterday starting at 2pm all through 5pm today, so I wasn't worried about how much snow we got today.

How bad is the icing down there? My dad called and said the roads were a mess.

Quoting TheRasberryPatch:Great pictures 717. the river burch didn't make it huh? snapped? sorry i wasn't around to help. i was out shoveling. UGH that was a pain. it was too wet for the snowblower. wow there was a lot of water under the ice

watch out for falling ice

Just got back from doing it myself. When I got home yesterday my son was actually showing iniative and shoveling without being asked. Of course it was the one time I didn't want him to. So he got the top half of our driveway, which is on a slope, done before I stopped him. I had a terrible time getting in the cars to start them and get them warming. Had to scrape and scrape to get it off that top half. Bottom and sidewalk were heavy but manageble with the big strong 15 year old to scoop it after I scraped it.

Great pictures 717. the river burch didn't make it huh? snapped? sorry i wasn't around to help. i was out shoveling. UGH that was a pain. it was too wet for the snowblower. wow there was a lot of water under the ice

We received around a half inch of sleet and .2-.3" of freezing rain here in northern Dauphin co. The sleet certainly saved us as I don't see any tree damage this morning (though it's likely there's some in the area). Power outages are minimal to none.

I finally found the help menu and might have it figured out. Let's see...

I did it. So here is my attempt at a measurement. I am 5 miles east of Harrisburg (at the corner of Union Deposit Rd and Nyes Rd for those who know the area). I'm kind of half way between Blizz and Raspberry.

pretty much a bust up here in New Milford CT. about 6" yesterday and very little ice this morning. roads are fine, a little slippery but basically wet. Only a thin film of ice on the car this morning. oh well

Thanks! Believe me I would NEVER plant another boxwood. We bought the house when it was 9 months old and it was already in. In our 100 year old house in Ewing, NJ before we moved here we had them on either side of the front door and they were a mess. I had this whole intricate support system for a while be for I finally gave up. My homeowners association says I have to have 5 shrubs/bushes so I will have to come up with something to put there.

I will keep you informed. I need to replace bushes this spring and the landscaper I deal with is pretty good. he usually has a good idea of what to plant especially for holding up in this climate.

Thanks! Believe me I would NEVER plant another boxwood. We bought the house when it was 9 months old and it was already in. In our 100 year old house in Ewing, NJ before we moved here we had them on either side of the front door and they were a mess. I had this whole intricate support system for a while be for I finally gave up. My homeowners association says I have to have 5 shrubs/bushes so I will have to come up with something to put there.

Ever try Japanese Holly (hoogendorn)? I hear you have to run water to soak the ground in the fall before the frost, no matter what shrub you have.

Quoting originalLT:Hoy, thanks for the info, but on my computer, I don't see that, right next to the refresh button is a button that if pushed, takes me back to my home page. Is there a different refresh button?

It looks like a piece of paper torn in two with jagged edges in the middle. You might have to look under tools, depending on what browser you are using. Just look for a "compatibility view" setting.

Nope, I think I'll be good :) The temperature just went above freezing and there's melting occurring. It's 32.7 and supposed to get to 40. It looks bad out there, but I just went for a walk and the sidewalks are walkable if you have tread on your boots. Streets are fine, just soaking wet with huge puddles. I'm assuming the runways must be fine also. I'll let you know if I get stuck in the airport for hours though. My only concern is the effect delays last night and early this morning might have on flights later in the day.

Morning everyone, Temp. got up to 32.5 by 7:45AM , I guess we got between .30-.40" of Ice, all school closed in Sw CT.. Rain just about over here. Good luck on your trip Hoy, enjoy the warm weather. P451, sounded like a bust for you, but not down here,we got just about what was forecasted, with maybe just alittle less snow amounts.

717Weather - i have like 5 boxwoods that were destroyed last year that i need to replace. the holes are so big. talking to a landscaper he said the boxwoods aren't great for snow and ice. i would look for another bush this spring that won't be so susceptible to winter damage

Thanks! Believe me I would NEVER plant another boxwood. We bought the house when it was 9 months old and it was already in. In our 100 year old house in Ewing, NJ before we moved here we had them on either side of the front door and they were a mess. I had this whole intricate support system for a while be for I finally gave up. My homeowners association says I have to have 5 shrubs/bushes so I will have to come up with something to put there.